Sandwich panels serving as floor panels for vehicles, especially those of a light construction for aeroplanes, are known per se. Balsa crosscut wood or hexagonal Nomex honeycombs are used as cores therefor. Both aluminium panels with a weight per unit area of 5 kg/m.sup.2 and fibre-reinforced plastics materials based on epoxy resin are known as cover or belt materials, as well, more recently, as phenol resins. The fibres--carbon, Kevlar or glass fibres--are inserted as several plies of unidirectional layers or bi-directional fabrics. Carbon fibre reinforced sandwich panels of known prior art weigh at least 2 kg/m.sup.2. The lightweight panels are mainly intended for use in aeroplanes in order to keep as low as possible the operating deadweight and, as a consequence thereof, the fuel costs. In the aeroplane industry, there are exact requirements for minimizing combustibility and for minimizing the density of smoke and the toxicity of materials. The values are measured and evaluated according to current standards. Epoxy resins do not meet these requirements. Modifications using chemicals permit the requirement regarding combustibility to be met, but the density of the smokes and the toxicity are also increased to an unacceptable level. Phenol resins, which have been used more recently since they meet the requirements regarding combustibility and also give off relatively few smoke, are inadequate, due to their mechanical properties, for forming the adhesive joint between the cover layer or core material, with the result that epoxy resin is inserted into this adhesive joint. With comparable combustibility, this panel figuration produces approximately half to one quarter of the smoke levels of a conventional, lightweight panel.
A fire-resistant wall has been disclosed in U.S. Pat. No. 3,518,156, wherein one outer layer is formed from a thermoset resin and the other outer layer is formed from metal. a fibre-reinforced layer is embedded in the wall on each side of the core. In the event of fire, the metallic layer cannot withstand a temperature of between 700.degree. C. and 800.degree. C.